Chronic inflammatory responses leading to destruction of synovial tissue is characteristic of rheumatoid arthritis (RA), an autoimmune disease of unknown etiology. Dendritic cells in the joint are likely to play a crucial role in initiating the disease by presenting peptide antigens derived from self proteins to autoreactive T cells. We have observed increased uptake by dendritic cells of IgGs bearing altered N-oligosaccharides, shown previously to be present in the serum and synovial fluid of RA patients. This suggests that modified IgG (G0 IgG) taken up by dendritic cells may be processed and presented via class II histocompatibility proteins quite efficiently, leading to a breakdown in tolerance of T cells reactive with IgG-derived peptides. To further characterize binding of G0 IgG to dendritic cells and test whether IgG-reactive T cells might contribute to the disease, we will perform the following experiments. In specific aim 1, novel assays will be developed which provide a highly sensitive means of detecting binding of G0 IgG to dendritic cells. IgG isotype will also be tested as a determinant of binding. Subcellular localization of internalized Go IgG will determined using electron microscopy, and intersection of G0 IgG with the class II h istocompatibiity processing pathway assessed using biochemical assays. In specific aim 2, receptors on the surface of dendritic cells responsible for binding G0 IgG will be identified using chemical crosslinking and gel electrophoretic analyses. In specific aim 3, T cells from patients and normal controls will be tested for proliferative responses to dendritic cells pulsed with G0 IgG. These experiments should determine if G0 IgG taken up by dendritic cells can be efficiently processed and presented via class II histocompatibility molecules to peripheral T cells which are potentially autoreactive.